The objective of the research proposed in this application is to develop and test an instrument for in vivo measurement of erythrocyte velocity and microspectrophotometry for oxyhemoglobin saturation determination. The field of microcirculatory research continues to be dependent upon the development of specialized instrumentation for measurement of microvascular hemodynamic variables. The commercial availability of an instrument which is accurate, easy to implement and of relatively low cost for measurement of red blood cell velocity and oxyhemoglobin saturation should significantly enhance the basic science and clinical research potential in this field. The objectives of Phase I are threefold: (1) to modify the velocimeter for detection of the direction of blood flow, (2) to extend its use to epiillumination and epifluorescence, and (3) to design a system for on-line microspectrophotometry. The long term objectives of Phase II are to (1) further develop the velocimeter for both clinical and research applications emphasizing simplicity and accuracy of operation, (2) implement and calibrate the microspectrophotometer for use in determination of oxygen saturation of hemoglobin in microvessels, with emphasis on using epiillumination. At this stage a simply operated instrument would be commercially available at a relatively low cost for the noninvasive simultaneous measurement of erythrocyte velocity and oxyhemoglobin saturation in microvessels.